Presently, much lighting used for applications such as rail lighting, for example, still uses incandescent light bulbs. However, incandescent light bulbs are inefficient and need to be replaced regularly. Some applications may use a very large number of incandescent light bulbs. As a result, if the light bulbs regularly fail, having a large number of incandescent light bulbs creates a high cost due to both the cost of the new bulb and labor associated with its replacement.
In addition, some lighting systems require the incandescent light bulbs to be electrically connected in series. Traditional incandescent light bulbs can be connected in series across an AC or DC power supply. This allows lights to be used where the only supply available may be much higher than the voltage rating of the lights. Since the impedance of the incandescent light bulbs is constant, each receives an equal share of the total voltage and so operate predictably. Furthermore, since a filament bulb is a resistive load when connected in a serial string across an AC supply, power factor is unity.
However, other types of light sources may not behave as a traditional incandescent light bulb behaves when connected in series. As a result, simply replacing an incandescent light bulb with another type of light source is not trivial. For example, other types of light sources may have features of their behavior that prevent proper operation if electrically connected in series.